The next time you are washing your hands and complain because the water temperature isn't just how you like it, think about how things used to be.
The wealthy had slate floors that would get slippery in the winter when wet, so they spread thresh (straw) on floor to help keep their footing. As the winter wore on, they added more thresh until, when you opened the door, it would all start slipping outside. A piece of wood was placed in the entranceway. Hence the saying a thresh hold.